The present invention relates to methods and apparatus for measuring the pressure of a gas without physical contact with said gas. More particularly, the present invention relates to a system of the above general type which permits the measurement of the pressure of a gas at a preselected small volume or point within a larger volume of the gas. Specifically, the invention relates to a sensing apparatus and method for measuring the pressure of a gas or vapor by focusing radiation on a small section of the gas, varying the intensity of said focused radiation from below an intensity level at which electrical breakdown occurs to a level at which breakdown occurs and monitoring the gas under test to detect electrical breakdown and the light intensity level at which such electrical breakdown occurs. The light intensity level at breakdown is then used to determine pressure of the gas by consulting a reference or characteristic curve for the gas or vapor under test which relates the intensity of radiation to pressure at breakdown. Such a characteristic curve could be developed by means of a separate experiment for the particular gas under test.
In many industrial processes it is desirable to know the local pressure of a gas at points within a reaction chamber in order to control or optimize the reactions or processes taking place within such chamber. It is important in many such processes to be able to measure the pressure of a gas without any physical intrusion into the environment which contains the gas so as to avoid any interference with the reaction process.
Generally, non-contacting pressure sensors are desirable in situations where information on the pressure of a gas is desired but contact with a gas is impractical for various reasons. Such a situation exists where the pressure of a gas at a specific reaction section in a chamber is desired and the gas exhibits a large pressure gradient across the larger volume of the reaction enclosure. In such a situation it is not practical, if not impossible, to rapidly locate and change the position of a sensor in the enclosure confining the gas. Moreover, the volume of the gas under study may be too small to use conventional techniques.
To overcome these and other problems, non-contacting sensors for measuring various properties of a gas have been developed. Several techniques are known which involve the projection of a beam of light toward a moving gas stream, detecting components of the beam reflected, scattered, or otherwise modified by the moving gas, and analyzing the effect of the motion upon the detected beam either independently of or in comparison with the transmitted beam. The above techniques are known to involve use of a laser for the projected beam and optical detection techniques for analyzing the frequency, intensity, or other changes in the beam brought about by the moving gas.